Automotive type lead-acid batteries have interlaced positive and negative electrodes, also called plates. Each plate consists of special material, known as active material, supported on lead-alloy grids. The active material is formed from lead oxide pastes which are processed to a firm, porous form.
In the preparation of plates for a lead-acid battery, a mixture is formed containing oxides of lead, a significant amount of metallic lead, sulfuric acid, water, and various additives. As a result of chemical reaction during mixing, a portion of the mixture is initially converted to lead sulfate (PbSO.sub.4), providing an active material precursor paste which includes lead and its oxides and sulfates.
The precursor paste is applied to conductive lead grids and, using conventional methods, the freshly pasted plates are then typically cured to stabilize the precursor material and to enhance the strength of the plates. Both positive and negative plates are made by the same basic process except for the selection of additives.
Typically, negative plates are cured for up to three days in a highly humid and warm air atmosphere to oxidize the free lead. Positive plates are cured by steam at near 100.degree. C. for 3 hours. Plates are assembled in the battery and formed in a multi-stage process which involves charging at a relatively high rate in several stages, each lasting several hours.
The curing steps of current processes are time consuming and often lead to irregular product quality because such curing often fails to fully oxidize lead. The achievement of being essentially lead-free (i.e. fully oxidized product) is a key feature of a high quality product.
Therefore, it is desirable to have a new process for preparing electrodes which produces a more consistent and lead-free product.